1. Field of the Invention
This invention relates to a seat having a seatback that can be lifted and lowered and adjusted in position with respect to a seat cushion in accordance with the physique of the occupant.
2. Description of the Related Art
A vehicle seat is known, which has a seatback which front surface (seat surface) is shaped in conformity with the back of the occupant, to make the occupant feel that his or her back well fit in the seat. To make another occupant feel comfortable in the vehicle seat, the seatback must be lifted or lowered in accordance with this occupant's physique, particularly the height, thus adjusting the seat surface of the seatback in terms of position.
Of most seats, the seatback is coupled at the lower edge to the rear edge of the seat cushion by a reclining device. Inevitably, the seatback cannot be lifted or lowered with respect to the seat cushion. This is why any vehicle seat, the seatback of which can be adjusted in position (i.e., seat surface) in accordance with the occupant's physique (height), is divided into upper and lower halves. The lower half of the seatback is coupled to the seat cushion, and the upper half of the seatback is lifted or lowered with respect to the lower half.
JP 2008-253609A, for example, discloses a seat. Of this seat, the seatback is divided into upper and lower halves. The lower half supports mainly the waist and lower ribs of the occupant. The upper half supports mainly the occupant's shoulder blades, and is coupled to the lower half and can be lifted and lowered. To the upper edge of the upper half of the seatback, a headrest is secured. The upper half of the seatback incorporates a height adjusting mechanism for adjusting the height of the headrest. The upper half of the seatback is coupled to a pair of stays of the headrest, and can be lifted or lowered as the headrest is lifted or lowered. As the height adjusting mechanism is manipulated, the headrest is lifted or lowered. The upper half of the seatback is thereby lifted or lowered to the position that accords with the occupant's physique (height). The upper half of the seatback is thus adjusted in terms of height.
The headrest can be lifted to a level higher than the upper half of the seatback, and can therefore reliably support the occupant's head even if the occupant is of large physique, having the head much spaced from the shoulder blades.
JP 2008-254645A discloses a seat, too. The seatback of this seat is also divided into upper and lower halves. The upper half of the seatback incorporates a height adjusting mechanism configured to lift and lower the seatback with respect to the lower half of the seatback, and also an angle adjusting mechanism configured to adjust the angle at which the upper half is inclined to the lower half. The height adjusting mechanism therefore lifts or lowers the upper half of the seatback to the position that accords with the occupant's physique. Thus, the upper half of the seatback is adjusted in height. The angle adjusting mechanism adjusts the inclination of the upper half of the seatback in accordance with the occupant's physique, not only setting the occupant's line of sight appropriately, but also making the occupant feel that his or her back well fit in the seat.
Another type of a seat is known, the seatback of which is isolated from the seat cushion, not coupled at lower edge to the rear edge of the seat cushion. JP 2012-143634A, for example, discloses an office seat, not a vehicle seat. The seat-cushion frame of this office seat is mounted on the base (i.e., riser), and an L-shaped support is secured by a link to the base and seat-cushion frame. The seatback is secured to the front of the seatback support. If the occupant sits shallow in the seat, the lower half of the seatback will move forward to support the occupant's waist. If the occupant sits deep in the seat, the lower half of the seatback will move backward, not preventing the occupant from sitting deep. Thus, the occupant feels well fit in the seat, whether he or she sits shallow or deep in the seat.
If the seatback is divided into upper and lower halves and if the lower half is coupled to the seat cushion and the upper half is lifted or lowered with respect to the lower half, the upper and lower halves will be spaced apart, providing a gap between them. In consequence, the occupant cannot feel well fit at the seat surface of the seatback.
A seat lifter may be provided between the riser (i.e., base) and the seat cushion. In this case, the distance between the lifted and lowered positions of the seatback, i.e., height-adjusting range, can be long that occupants of various physique may feel well fit in the seat. If the seat lifter is driven, however, not only the seat cushion and the seatback will be lifted or lowered, but also the top surface (seat surface) of the seat cushion and the front surface (seat surface) of the seatback will move forward or backward. As a result, the occupant cannot feel well fit at the seat surface of the seatback.
If the lower edge of the seatback is not coupled to the rear edge of the seat cushion and the seatback is spaced apart from the seat cushion, the occupant can feel that the waist is well fit in the seat, whether sitting shallow or deep in the seat. However, the seatback is not configured to lift or lower.
If isolated from the seat cushion, the seatback can indeed be lifted and lowered and can be adjusted in position (i.e., position of its seat surface) in accordance with the occupant's physique. If the seatback is lifted or lowered, however, its lower half supporting the occupant's waist will change in position, failing to make the occupant to feel that the waist is well fit in the seat. The configuration in which the seatback can be lifted and lowered cannot be employed.
In any conventional configuration described above, the seatback cannot be adjusted in position in accordance with the occupant's physique, inevitably failing to make the occupant feel well fit at the seat surface.
An object of this invention is to provide a seat in which the seatback can be adjusted in position (at its seat surface) in accordance with the occupant's physique to enable the occupant to feel well fit at the seat surface.